The Singapore company, which provides semiconductor packaging design and assembly solutions, had said in May that it had received approaches by some companies but had not identified them.

"The company wishes to confirm that these parties include JCET and Huatian. There is no assurance that any of these approaches will result in any definitive agreement or transaction," it said in a statement on Thursday.

The Chinese companies, which were first named by Bloomberg news on Wednesday, each have a market capitalisation that is only slightly bigger than STATS ChipPAC.

STATS ChipPac's shares shot up 12 percent higher on Wednesday and were flat on Thursday. The stock has doubled this year on the view that it was a takeover target for Taiwanese or Chinese firms.

Moody's Investors Service cut its ratings for the company this month, citing its debt load as well as slowing growth in the high-end communications segment and muted demand from the personal computer and consumer-end markets. It noted that revenues have been on a declining trend since 2011.

STATS ChipPAC's corporate family rating and senior unsecured debt rating was cut to Ba2 from Ba1.

Temasek in early 2007 made a bid of up to $1.6 billion for the 64.4 percent of STATS ChipPAC it did not own, but it was unable to hit the 90 percent mark which would have allowed a delisting. It currently owns 83.8 percent of Stats ChipPAC, according to Thomson Reuters data.